1. Field
Embodiments of the present invention generally relate to a method and apparatus for chemical mechanical polishing (CMP) of semiconductor substrates, and more particularly to temperature control during such chemical mechanical polishing.
2. Description of the Related Art
Integrated circuits are typically formed on substrates, such as silicon wafers, by the sequential deposition of various layers such as conductive, semiconductor or insulating layers. After a layer is deposited, a photoresist coating can be applied on top of the layer. A photolithographic apparatus, which operates by focusing a light image on the coating, can be used to remove portions of the coating, leaving the photoresist coating on areas where circuitry features are to be formed. The substrate can then be etched to remove the uncoated portions of the layer, leaving the desired circuitry features.
As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate tends to become increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. For example, the ability to focus the light image on the photoresist layer using the photolithographic apparatus may be impaired if the maximum height difference between the peaks and valleys of the non-planar surface exceeds the depth of focus of the apparatus. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. Chemical mechanical polishing typically includes mechanically abrading the substrate in a slurry that contains a chemically reactive agent. During polishing, the substrate is typically held against a polishing pad by a carrier head. The polishing pad may rotate. The carrier head may also rotate and move the substrate relative to the polishing pad. As a result of the motion between the carrier head and the polishing pad, chemicals, which can include a chemical solution or chemical slurry, planarize the non-planar substrate surface by chemical mechanical polishing.
The CMP process, designed to remove nonplanarity, nevertheless can lead to non-planar artifacts. For example, the fluid dynamics of the slurry, coupled with the mechanical aspects of the system can lead to turbulence variations across the polishing pad/substrate, proportional to the relative speed of rotation. These turbulence variations are believed to lead to erosion in the substrate which can result in deviations from planarity, contrary to the goal of the CMP. This erosion can be countered in part by also moving the substrate in relation to the CMP polishing pad, but such erosion is not entirely eliminated. Another defect or deviation in planarity which can arise from CMP is “dishing” or differential polishing and/or erosion which occurs between different material layers, typically material layers of different hardness. For example, when CMP breaks through an overlying hard layer (e.g., an oxide), an underlying layer of softer metal can be “dished.” Consequently, there is a need in the art to improve the ability of CMP to planarize a substrate and to reduce non-planar side-effects of CMP such as erosion and dishing.